<p>This study presents a failure analysis of a leaking 304 stainless steel pipeline used for liquid caustic soda transportation. The failed pipe section was characterized using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), industrial computed tomography (CT), x-ray diffraction (XRD), and metallographic optical microscopy. Immersion tests were conducted to validate the role of inclusions in the promotion of failure. The results demonstrate that the leakage originated from pits formed by the synergistic action of pitting corrosion and intergranular corrosion (IGC) on the inner pipe wall. Locally distributed large-sized FeCr₂O₄ inclusions on the inner wall surface compromised the integrity of the passive film, with crevices between these inclusions and the matrix providing pathways for chloride ion (Cl^–) ingress. The pipeline was pressure-tested using tap water, in which the Cl^– concentration significantly exceeding the permissible limit specified by the standard. Incomplete drainage posttest left residual tap water inside the pipeline, initiating pitting corrosion at the inclusion sites. Furthermore, sensitization of the pipeline base material reduced its resistance to both IGC and pitting corrosion, accelerating the propagation of the corrosion pits. This study provides technical guidance for material selection and installation of chemical process piping systems.</p>